The invention relates to the maintenance of bond collets during semiconductor die bonder production runs, and in particular to the cleaning of the bond collets.
Typically, a wafer comprising a plurality of semiconductor dice are mounted on an adhesive film during singulation wherein each individual die is separated while adhering to the adhesive film. Detaching and picking up of a die from the adhesive film is thus commonly involved in die bonding and flip chip bonding processes for assembling an electronic package.
In a flip chip process, dice are picked up by a flip arm at the back sides of the dice and then transferred to a bond head comprising a bond collet, so that the bond collet picks the dice from the bump side of the dice. As the bump dice are mounted on a wafer film from the bump side, there are often adhesive residues on the bump surface after detaching the dice from the adhesive film. Since the bond collet directly contacts the bump side of the dice during die transfer to the bond head, adhesive residues will eventually transfer and accumulate on the bond collet surface, affecting bonding quality. Also, an unclean bond collet surface may damage the die surface.
Typically, in a flip chip assembly process, the bond collet is cleaned as a manual offline process at fixed intervals. Most commonly, the bond collets are cleaned by a solvent and a clean room cloth by machine operators. The cleanliness is visually judged by the operators. During bond collet cleaning, the machine has to be stopped and this frequency can reach up to five times per hour, which affects the utilization of the machine and decreases productivity. Therefore, it is desirable to shorten the cleaning time.
Examples of prior art for bond collet cleaning application in a die bonder are highlighted as follows. Korean patent KR 20020039571A entitled “System and method for cleaning bond collet” discloses a system that cleans a bond collet by a blower and a brush. In the cleaning system, the bond collet is transferred to a position above a working table by a transferring arm. The working table supports a remover, such as a brush, for cleaning the bond collet. The transferring arm then rubs the bond collet on the remover with air blowing out of the bond collet to remove the chip residues, with controller control. The disadvantage of this method is that the air blown may blow particles to the bond area, and damage to the bond collet tip may be caused by rubbing against the stiff bristles of the brush.
Japanese patent JP 04-159734A entitled “Collet cleaning method and die bonder” discloses a bond collet cleaning setup in a die bonder which cleans a bond collet during every die-bonding operation. This published patent application discloses two setups. In the first setup, a motor driven rotary cleaning block with eight spiral blades is placed in between a wafer ring and a lead frame. The collet picks up a die from the wafer and places the die on lead frame islands. After that it moves to the cleaning block position and let the spiral blades remove the residue. A new bonding cycle begins after the cleaning process. The second setup is a cheaper version of the first setup, in that the rotary cleaning block is replaced by a fixed cleaning block. Again, this method might also generate contaminants to the bond area and cause bond collet damage.